1. Field of the Invention
This invention relates to a field of earth boring and in particular to both method and apparatus aspects of boring a large size blind hole through hard or soft earth formations.
2. Description of the Prior Art
A large number of different types of machines have been proposed for mechanically excavating mine shafts and other relatively large vertical blind holes in earth formations. However, prior attempts to develop such a machine have been generally unsuccessful. For the most part mine shafts and other vertical blind holes are still excavated by drilling and blasting.
Examples of prior art shaft forming machines are shown by the following U.S. Pat. Nos.: 1,132,510, granted Mar. 16, 1915, to Karl Borschutzby; 1,175,952, granted Mar. 21, 1916, to H. G. Hase; 1,406,349; granted Feb. 14, 1922, to Clyde S. Corrigan; 1,988,414, granted Jan. 15, 1935, to P. Bogoutsky; 2,221,226, granted Nov. 12, 1940, to O. M. Wick; 2,769,614, granted Nov. 6, 1956, to Victor Zeni; 2,819,038, granted Jan. 7, 1958, to John E. Eckel; 3,185,226, granted May 25, 1965, to Richard J. Robbins; 3,379,264, granted Apr. 23, 1968, to Kenneth C. Cox; 3,497,021, granted Feb. 24, 1970, to Charles W. Burrell; 3,547,211, granted Dec. 15, 1970, to Alfred W. Christensen and Richard L. Marsing; 3,593,811, granted July 20, 1971, to Jack V. Tedrow; 3,695,370, granted Oct. 3, 1972, to Kenneth W. Jones; and 3,710,878, granted Dec. 4, 1970, to Masaaki Endo, Mituo Miura and Namoru Shinozaki.